1. Field of the Invention
The present invention relates generally to a method and apparatus for providing voice and data services in a mobile communication system. In particular, the present invention relates to a method and apparatus for providing an integrated voice/data service in a network environment in which various access networks overlap each other.
2. Description of the Related Art
Mobile communication systems have developed from 1st Generation (1G) and 2nd Generation (2G) systems which chiefly provide a voice service using a circuit network into an International Mobile Telecommunication-2000 (IMT-2000) system which is a 3rd Generation (3G) digital mobile communication system. The IMT-2000 system, unlike the 1G and 2G mobile communication systems, provides a packet data service for allowing subscribers to access the mobile Internet in a wide-spread mobile communication environment. In case of a Code Division Multiple Access 1X (CDMA2000 1X) system, which is related to the IMT-2000 system, a user accessing an Internet Protocol (IP) network via a wireless access network can receive a data service at a rate of a maximum of 153.6 Kbps, and in case of First Evolution-Data Only (1x EV-DO) system, the user can receive a data service at a rate of a maximum of 2.4 Mbps. However, the mobile communication network has limitations in providing a high-speed packet data service.
Recently, with the evolution of the mobile communication environment, various wireless access technologies such as Wireless LAN or High Performance Local Area Network version 2 (HiperLAN/2) based on IEEE 802.11x and Bluetooth have been proposed. Such technologies, although they cannot guarantee mobility up to the level of the cellular mobile communication system, were proposed as an alternate for providing a high-speed data service in a hot spot zone including public places or in a home network environment, replacing the fixed networks such as cable modems or Digital Subscriber Line (xDSL)-based networks. For example, an IEEE 802.1b-based wireless LAN provides a data rate of about 11 Mbps at a 2.4-GHz ISM band, and an IEEE 802.11a-based wireless LAN provides a data rate of a maximum of 54 Mbps at a 5-GHz ISM band, enabling a high-speed wireless data service with the low cost.
Such wireless access technologies, although they provide a high data rate, have limitations in providing public network-based services due to extremely limited mobility, a narrow coverage and interference, caused when a high-speed data service is provided with the wireless LAN. In order to cope with these limitations, studies are being conducted on wireless Metropolitan Area Network (MAN) technology developed by benefiting from advantages and compensating for disadvantages of the cellular mobile communication system and the Wireless LAN system. A 2.3-GHz band High-speed Portable Internet (HPi) system, a typical example of the Wireless MAN technology, can provide a throughput of 50 Mbps per cell using various types of access terminals in a stationary indoor/outdoor environment and a mobile environment for a pedestrian speed and a mid/low speed (about 60 Km/h). In addition, the HPi system supports a wide-range data rate according to conditions of a radio channel.
However, as the wireless access technologies for providing various data rates and mobilities in a wireless environment are standardized, it is necessary to provide a service capable of meeting various user's demands by benefiting from advantages and compensating for disadvantages of different technologies. Further, in order to provide such a service, it is necessary to seamlessly provide voice and data services to a user who accesses a serving network via an optimal access network.
Recently, with the rapid development of communication technology and the sharp increase in users' demands, efforts are being made to integrate a circuit network-based voice service with a packet network-based data service into a multimedia service through the Internet. As an example of the multimedia service, there is a Voice over Internet Protocol (VoIP) technology for transmitting voice via the Internet. Recently, ITU-T and IETF committees have led standardization on the VoIP technology and introduced various technologies. Along with such a tendency, next-generation mobile communication standardization organizations including 3rd Generation Partnership Project (3GPP) and 3GPP2 committees are conducting standardization on technologies capable of defining a configuration of an IP-based integrated network and providing a multimedia service to mobile subscribers. As yet, however, the technologies cannot guarantee quality-of-service (QoS) for a voice service provided in the IP network, and cannot achieve QoS higher than that of a voice service provided in the existing public switched telephone network (PSTN). In particular, when a VoIP service is provided in a wireless environment, considerable effort and cost are needed to secure stable QoS while providing a user with wide-range mobility. Therefore, although the VoIP technology is highly developed, the VoIP service is expected to gradually evolve from the existing PSTN-based voice service. Even after the completion of standardization on an All-IP network, because the PSTN-based voice service will be continuously used, there is a demand for interworking between a circuit network and a packet network.